The invention relates to omni-directional sensors and more specifically to mechanical omni-directional sensors which are suitable for applications such as seat belt restraints.
Acceleration sensors are used for many purposes. One widespread use is in automobiles for locking seat belts automatically upon detection of a predetermined positive or negative acceleration (deceleration). Such sensors are also used to inflate vehicular air bags when a specific, higher predetermined vehicle deceleration occurs.
One previous prior art design is disclosed in U.S. Pat. No. 5,636,807 issued to Warrick. This disclosure identifies a mechanical acceleration sensor that incorporates a heavy inertia mass suspended by two balls which are supported by two pivoting arms and supporting linkage.
Many automotive acceleration sensors have an inertia mass which senses acceleration in the generally horizontal directions of travel of the automobile. This mass can take the form of a tilting mass, a swinging pendulum, or a ball rolling up a ramp. In all, a mechanism responds to a predetermined movement of the mass to lock the reel which stores the belt webbing to prevent webbing payout.
Another application for deceleration sensors is to lock aircrew safety harness seat belt reels in response to aircraft acceleration. Since aircraft travel in multiple directions (combinations of vertical and horizontal), the automotive inertia mass movement types of sensors, described above, would be only partially effective, since they are limited in operability to sensing acceleration in generally horizontal directions, or in the plane of vehicle movement.
Most aircraft (and some automotive acceleration) sensors operate by sensing a predetermined acceleration of the storage reel as the harness webbing attempts to unreel from it. This results from aircraft movement which imposes unseating “G” forces on an aircrew member. These sensors sometimes use weights or masses which move sufficiently radially at a predetermined reel speed to actuate a locking mechanism.
Other aircraft sensors use an inertia mass connected to the reel by a screw mechanism. Acceleration of the reel by unwinding webbing accelerates the mass which, due to inertia, lags rotary movement of the reel. This relative motion turns the screw which moves a locking dog axially to engage the reel ratchet teeth and lock the reel. Such an aircraft acceleration sensor is illustrated in U.S. Pat. No. 4,801,105 issued to Frisk.
Such aircraft acceleration sensors do not react directly to vehicle acceleration, but only indirectly by reacting to resultant web and reel acceleration. Since they only indirectly respond to vehicle acceleration, they require some web payout to operate. Also, these types of sensors are use-specific, i.e. useful only with webbing reels or other reactive secondary movements, and cannot be utilized to perform other functions.